Conventionally, a plurality of storage tanks at service stations or similar locations are buried underground in a side by side arrangement. For environmental purposes, a vapor recovery system fitted to delivery tank trucks is generally used in conjunction with the filling of the storage tanks wherein a common vent line is connected to each storage tank. One end of the common vent line is adaptable for connection to a fuel truck. Each tank has its own separate vent leading to the common vent line. In a multiple tank arrangement with a common vent line, it is very important that the gasoline or other liquid fluid from one tank does not escape into the common vent line and thereby contaminate an adjacent tank. Therefore, it is desirable to have a valve for each fuel tank which is normally open to permit the passage of vapor, but closed to prevent passage of liquid fuel therethrough. It is further desirable to have a valve that is not complex. In addition, it is desirable to have a valve that responds quickly to the rise of liquid fuel within the valve.
Therefore, it is an object of this invention to provide an overflow valve which addresses these aforementioned concerns.